Issue |
A&A
Volume 474, Number 2, November I 2007
|
|
---|---|---|
Page(s) | 491 - 494 | |
Section | Galactic structure, stellar clusters, and populations | |
DOI | https://doi.org/10.1051/0004-6361:20077985 | |
Published online | 04 September 2007 |
White dwarf atmosphere models with Ly-alpha opacity in the analysis of the white dwarf cooling sequence of NGC 6397
Lehrstuhl für Theoretische Chemie, Ruhr-Universität, 44780 Bochum, Germany e-mail: piotr.kowalski@theochem.ruhr-uni-bochum.de
Received:
31
May
2007
Accepted:
27
June
2007
Aims.
We discuss the importance of pure hydrogen white dwarf atmosphere models with Ly- far red wing
opacity in the analysis of the white dwarf cooling sequence of the
globular cluster NGC 6397.
Methods.Our recently improved atmosphere models account for the previously missing opacity from the Ly- hydrogen line broadened by collisions
of the absorbing hydrogen atoms with molecular and atomic hydrogen. These models are the first
that well reproduce the UV colors and spectral energy distributions of cool white dwarfs with
K observed in the Galactic Disk.
Results.Fitting the observed magnitude and
color we obtained a value for the true distance modulus,
, that is in agreement with recent analyses.
We show that the stars at the end of the cooling sequence appear to be ~160 K cooler
when models that account for Ly-
opacity are used.
This indicates that the age of NGC 6397 derived from the white dwarf cooling sequence using atmosphere models that do not include the
correct Ly-α opacity is underestimated by ~0.5 Gyr.
Conclusions.Our analysis shows that it is essential to use white dwarf atmosphere models with Ly- opacity
for precise dating of old stellar populations from white dwarf cooling sequences.
Key words: stars: white dwarfs / stars: atmospheres / Galaxy: globular clusters: individual: NGC 6397
© ESO, 2007
Current usage metrics show cumulative count of Article Views (full-text article views including HTML views, PDF and ePub downloads, according to the available data) and Abstracts Views on Vision4Press platform.
Data correspond to usage on the plateform after 2015. The current usage metrics is available 48-96 hours after online publication and is updated daily on week days.
Initial download of the metrics may take a while.